This invention relates to a clutch system of the friction type placed in a power transmission system. Typical clutch systems include a clutch input such as a clutch basket, a clutch output such as a center clutch, and one or more plates making up a clutch pack and disposed between the clutch input and clutch output. When the clutch pack is compressed, the clutch input and clutch output become rotationally coupled. More particularly, it is a device for automatically engaging or disengaging a clutch based upon engine speed.
Most motorcycles incorporate a manual transmission coupled to the engine via a multi-plate clutch assembly. Typically, the multi-plate clutch is engaged/disengaged by the driver via a lever mounted on the handlebar. Although the lever operated clutch allows the driver to control the clutch engagement/disengagement, often times motorcycle drivers find the clutch lever difficult to operate smoothly. New riders have difficulty adjusting to smoothly engaging the clutch while operating the throttle to move the vehicle from a standing start. Experienced riders may need to partially disengage the clutch when traveling slowly to allow the engine to continue running without stalling. Motorcycle racers often have a difficult time controlling the engagement of the clutch and the application of the throttle to maximize acceleration. Off-road motorcycle racers often need to stop the rear wheel suddenly with the rear brake, causing the engine to stall if the clutch is not first disengaged. An automatic clutch can help overcome many of the problems associated with a manual clutch.
Automatic clutches for motorcycles have existed for more than 30 years, primarily for entry-level motorcycles with low power. More recently, retrofit automatic clutches for high-performance motorcycles have become available. Automatic clutches for high-performance motorcycles have many advantages over manual clutches. Currently available retrofit automatic clutches have several disadvantages:
Require replacement or changes to existing clutch parts. Most motorcycle clutch's pressure plates are spring loaded and attached to the center clutch. However, the centrifugal mechanism must spin with the clutch's outer basket which is coupled rotationally to the engine to provide clutch engagement force. Many existing retrofit automatic clutches require a modified clutch outer basket to bolt the new centrifugal pressure plate to.
Clutch lever override not possible at high engine speeds. Existing retrofit automatic clutches use a rigid centrifugal engagement mechanism. To disengage the clutch, the entire force of the centrifugal engagement mechanism must be overcome. At higher engine speeds, the increased centrifugal force of the engagement mechanism becomes difficult or impossible to overcome.
Clutch lever override has an inconsistent feel. Existing automatic clutches incorporate a clutch release mechanism that pushes against the centrifugal mechanism to release the clutch engagement. At low engine speeds, centrifugal force is low and the effort to release clutch engagement is low. At higher engine speeds, centrifugal force is high and the effort to release clutch engagement is high. Inconsistent clutch lever effort makes it difficult to effectively control manual override of the automatic clutch over different engine speeds.
Too much centrifugal force at high engine speeds. The stock non-automatic, non-centrifugal pressure plate provides a fixed amount of pressure to the clutch disks. The stock pressure plate force is limited to ensure the clutch can slip if excessive force is sent through the driveline. Existing retrofit automatic clutches transfer all of the force generated by centrifugal engagement mechanism into the clutch disks. At higher engine speeds, the excess centrifugal force can prevent the clutch from slipping in the event an excessive force is sent through the driveline. The excessive force traveling through the clutch may cause a failure in the engine or transmission.
Difficult to install automatic clutch. Most automatic clutches require many or even most of the OEM manual clutch components be replaced with the automatic clutch components. This requires time and cost to install the clutch. Also, it may be desirable for the motorcycle user to be able to switch back and forth between an automatic motorcycle clutch and a manual motorcycle clutch. A need exists for a clutch system that can easily be converted from automatic to manual operation and back again.
Difficult to adjust automatic clutch. Existing automatic clutches require that the gap between the clutch plates and the centrifugal mechanism be maintained to precise tolerances. Adjusting this tolerance may require swapping in different thickness clutch plates or somehow shimming the centrifugal mechanism. Additionally, clutch lever override performance may be optimized by very precisely adjusting the gap between the centrifugal mechanism and clutch plates. A need exists for easily and precisely adjusting the gap between the centrifugal mechanism and the clutch plates.
Adjusting the engine speed at which the clutch begins to engage and how quickly the clutch becomes fully engaged is important for proper operation of an automatic clutch. Existing automatic clutches require changing or shimming springs within the automatic clutch to adjust the engagement speed. Changing or shimming the engagement speed springs typically involves working with small fasteners within the confines of the engine. The operator may drop a small part in the engine requiring significant time and effort to retrieve the dropped piece.
Other automatic clutch solutions exist but all of the prior art fails to address all of the needs described.